In thermodynamics In science, thermodynamics is the study of energy conversion between heat and mechanical work, and subsequently the macroscopic variables such as temperature, volume and pressure, the term exothermic ("outside heating") describes a process or reaction that releases energy In physics, energy is a quantity that is often understood as the ability to perform work. This quantity can be assigned to any particle, object, or system of objects as a consequence of its physical state usually in the form of heat In physics and thermodynamics, heat is the process of energy transfer from one body or system to another due to thermal contact, which in turn is defined as an energy transfer to a body in any other way than due to work performed on the body, but also in the form of light Light is electromagnetic radiation of a wavelength that is visible to the human eye . In physics, the term light sometimes refers to electromagnetic radiation of any wavelength, whether visible or not (e.g. a spark, flame, or explosion), electricity Electricity is a general term that encompasses a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning and static electricity, but in addition, less familiar concepts, such as the electromagnetic field and electromagnetic induction (e.g. a battery), or sound Sound is a travelling wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations(e.g. burning hydrogen). Its etymology stems from the Greek prefix ex- (meaning "outside") and the Greek word thermein (meaning "to heat"). The term exothermic was first coined by Marcellin Berthelot Marcellin Pierre Eugène Berthelot (25 October 1827 – 18 March 1907) was a French chemist and politician noted for the Thomsen-Berthelot principle of thermochemistry . He synthesized many organic compounds from inorganic substances and disproved the theory of vitalism. He is considered as one of the greatest chemists of all time. The opposite of an exothermic process is an endothermic In thermodynamics, the word endothermic describes a process or reaction that absorbs energy in the form of heat. Its etymology stems from the Greek prefix endo-, meaning “inside” and the Greek suffix –thermic, meaning “to heat”. The opposite of an endothermic process is an exothermic process, one that releases energy in the form of heat process, one that absorbs energy in the form of heat.
The concept is frequently applied in the physical sciences Physical Science is an encompassing term for the branches of natural science and science that study non-living systems, in contrast to the biological sciences. However, the term "physical" creates an unintended, somewhat arbitrary distinction, since many branches of physical science also study biological phenomena to chemical reactions A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, often coming about only after the input of some type of energy, viz. heat, light or electricity. Classically, chemical reactions encompass, where chemical bond energy In chemistry, bond energy is a measure of bond strength in a chemical bond. It is the heat required to break Avogadro's number of molecules into their individual atoms. For example, the carbon-hydrogen bond energy in methane E(C–H) is the enthalpy change involved with breaking up one molecule of methane into a carbon atom and 4 hydrogen radicals is converted to thermal energy In thermodynamics, the internal energy of a thermodynamic system, or a body with well-defined boundaries, denoted by U, or sometimes E, is the total of the kinetic energy due to the motion of particles and the potential energy associated with the vibrational and electric energy of atoms within molecules or crystals. It includes the energy in all (heat).
Contents |
Overview
Exothermic refers to a transformation in which a system releases energy (heat) to the surroundings:
- Q < 0
When the transformation occurs at constant pressure:
- ∆H < 0
and constant volume:
- ∆U < 0
In an adiabatic Adiabatic heating or cooling of a gas results from pressure change. Work is done on or by the gas, but there is no heat transfer with the environment. Heat can be supplied to the gas by friction however. If an adiabatic process is frictionless too, the process is reversible and can be called isentropic system (e.g. a system that does not give off heat to the surroundings), an exothermic process results in an increase in temperature.[1]
In chemical reactions, the heat that is absorbed is in the form of electromagnetic energy. The loss of kinetic energy via reacting electrons causes light to be released. This light is equivalent in energy to the stabilization energy of the energy for the chemical reaction, i.e. the bond energy. This light that is released can be absorbed by other molecules in solution to give rise to molecular vibrations or rotations, which gives rise to the classical understanding of heat. In contrast, when endothermic reactions occur, energy is absorbed to place an electron in a higher energy state, such that the electron can associate with another atom to form another chemical complex. The loss of energy within solution is absorbed by the endothermic reaction and therefore is a loss of heat. This is the physical understanding of exothermic and endothermic reactions within solution.
Examples
A thermite reaction using Iron(III) OxideSome examples of exothermic processes are:[2]
- Condensation of rain from water vapor
- Combustion of fuels Fuel is any material that can be used to generate energy to produce mechanical work in a controlled manner. The processes used to convert fuel into energy include chemical reactions, such as combustion, and nuclear reactions, such as nuclear fission or nuclear fusion. Fuels are also used in the cells of organisms in a process known as metabolism such as wood Wood is a hard, fibrous tissue found in many plants. It has been used for centuries for both fuel and as a construction material for several types of living areas such as houses. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression. In the strict sense wood is produced as, coal Coal is a readily combustible black or brownish-black sedimentary rock normally occurring in rock strata in layers or veins called coal beds. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure. Coal is composed primarily of carbon along with variable and oil An oil is any substance that is liquid at ambient temperatures and is hydrophobic but soluble in organic solvents. Oils have a high carbon and hydrogen content and are nonpolar substances. The general definition above includes compound classes with, and uses, including vegetable oils, petrochemical oils, and volatile essential oils. All oils can
- Mixing water and strong acids More precisely, the acid must be stronger in aqueous solution than hydronium ion, so strong acids are acids with a pKa > −1.74 . This generally means that in aqueous solution at standard temperature and pressure, the concentration of hydronium ions is equal to the concentration of strong acid introduced to the solution. While strong acids are
- Mixing alkalis In chemistry, an alkali is a basic, ionic salt of an alkali metal or alkaline earth metal element. Some authors also define an alkali as a base that dissolves in water. A solution of a soluble base has a pH greater than 7. The adjective alkaline is commonly used in English as a synonym for base, especially for soluble bases. This broad use of the and acids An acid in common usage is a substance that tastes sour, reacts with metals and carbonates, turns blue litmus paper red, and has a pH less than 7.0 in its standard state. Examples include acetic acid (in vinegar) and sulfuric acid (used in car batteries). Acid/base reactions differ from redox reactions in that there is no change in oxidation state
- The setting of cement In the most general sense of the word, a cement is a binder, a substance that sets and hardens independently, and can bind other materials together. The word "cement" traces to the Romans, who used the term opus caementicium to describe masonry resembling modern concrete that was made from crushed rock with burnt lime as binder. The and concrete Concrete is a construction material composed of cement and other cementitious materials such as fly ash and slag cement, aggregate (generally a coarse aggregate made of gravels or crushed rocks such as limestone, or granite, plus a fine aggregate such as sand), water, and chemical admixtures
- Some polymerisation In polymer chemistry, polymerization is a process of reacting monomer molecules together in a chemical reaction to form three-dimensional networks or polymer chains. There are many forms of polymerization and different systems exist to categorize them reactions such as the setting of epoxy resin Epoxy or polyepoxide is a thermosetting polymer formed from reaction of an epoxide "resin" with polyamine "hardener". Epoxy has a wide range of applications, including fiber-reinforced plastic materials and general purpose adhesives
- Thermite Thermite is a pyrotechnic composition of a metal powder and a metal oxide, which produces an aluminothermic reaction known as a thermite reaction. Most varieties are not explosive, but can create short bursts of extremely high temperatures focused on a very small area for a short period of time reaction
Implications for chemical reactions
Main article: exothermic reaction An exothermic reaction is a chemical reaction that releases energy in the form of heat. It is the opposite of an endothermic reaction. Expressed in a chemical equation:Chemical exothermic reactions are generally more spontaneous than their counterparts, endothermic reactions. In a thermochemical reaction that is exothermic, the heat may be listed among the products of the reaction.
See also
- Calorimetry Calorimetry is the science of measuring the heat of chemical reactions or physical changes. Calorimetry is performed with a calorimeter. The word calorimetry is derived from the Latin word calor, meaning heat. Scottish physician and scientist Joseph Black, who was the first to recognize the distinction between heat and temperature, is said to be
- Chemical thermodynamics Chemical thermodynamics is the study of the interrelation of heat and work with chemical reactions or with physical changes of state within the confines of the laws of thermodynamics. Chemical thermodynamics involves not only laboratory measurements of various thermodynamic properties, but also the application of mathematical methods to the study
- Differential scanning calorimetry Differential scanning calorimetry or DSC is a thermoanalytical technique in which the difference in the amount of heat required to increase the temperature of a sample and reference is measured as a function of temperature. Both the sample and reference are maintained at nearly the same temperature throughout the experiment. Generally, the
- Endergonic Endergonic means "absorbing energy in the form of work." Endergonic reactions are not spontaneous. By thermodynamic standards, work, a form of energy, is defined as moving from the surroundings (the external region) to the system (the internal region). Thus, an endergonic process, as contrasted with an exergonic process, is one wherein
- Endergonic reaction In chemical thermodynamics, an endergonic reaction is a chemical reaction in which the standard change in free energy is positive, and energy is absorbed. In layman's terms the total amount of energy is a loss (it takes more energy to start the reaction than what you get out of it) so the total energy is a negative net result. For an overall gain
- Exergonic Exergonic means to release energy in the form of work. Its etymology stems from the suffix -ergonic, as derived from the Greek root ergon, meaning work, combined with the Greek prefix ex-, meaning out of. By thermodynamic standards, work, a form of energy, is defined as moving from the system to the surroundings (the external region). Thus, an
- Exergonic reaction
- Endothermic reaction
External links
- http://chemistry.about.com/b/a/184556.htm Observe exothermic reactions in a simple experiment
References
- ^ Perrot, Pierre (1998). A to Z of Thermodynamics. Oxford University Press. ISBN The International Standard Book Number is a unique numeric commercial book identifier based upon the 9-digit Standard Book Numbering (SBN) code created by Gordon Foster, now Emeritus Professor of Statistics at Trinity College, Dublin, for the booksellers and stationers W.H. Smith and others in 1966 0-19-856552-6.
- ^ Exothermic - Endothermic examples
Categories: Thermodynamics Thermodynamics concerns the physics of heat, work, temperature, energy, and entropy | Chemical thermodynamics
unknown
Mon, 16 Aug 2010 06:02:18 GM
"Is Hell . exothermic. (gives off heat) or endothermic (absorbs heat)? Support your answer with a proof." Most of the students wrote proofs of their beliefs using Boyle's Law (gas cools off when it expands and heats up when it is ...
